AA215 diode I used for the design circuit only. The real diode is 1N34A. How to calculate the gain defined by C8,R6 and R12? What does it means, VCO that operates out of frequency range? What is the purpose of TR3, is it used as amplifier too? Why it need used 4.7k
audioguru2
- Apr 6, 2004
- 12,026
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- Apr 6, 2004
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- 12,026
Hi Badai,
1) The project specifies using a microwave transistor and diode, you are using a general purpose 250MHz transistor and high frequency diode.
2) The DC gain of opamp A1 in the project is usually defined as the ratio of resistors R6 (1M) divided by R12 (220) if the circuit is driven from a very low impedance. However the driving source impedance is not low in this circuit and adds to the R12 resistance reducing the gain of the opamp. At maximum sensitivity setting, R5 (560) and R2 (470) are in series with R12 so the DC gain is 800.
3) C8 (10nF) across R6 (1M) cuts-off frequencies above 16Hz, so A1 will have a maximum gain of 800 at about 3.2Hz, 566 at 16Hz, 400 at 32 Hz and 200 at 64Hz etc.
4) The article should say, "The VCO operates through-out the audio-frequency range".
5) TR3 is used as a current amplifier and drives the speaker through R4, since the power output of A3 is not nearly enough to drive a speaker.
6) The 4.7K pot is the project's sensitivity control and is adjusted so that the circuit ignores external electromagnetic fields (from mains wiring and local AM, FM and TV stations).
7) The 8 ohm speaker produces the tone from the VCO. The higher the pitch, then the higher is the signal level that the project is picking-up. This project is not a radio and will not reproduce voices.
1) The project specifies using a microwave transistor and diode, you are using a general purpose 250MHz transistor and high frequency diode.
2) The DC gain of opamp A1 in the project is usually defined as the ratio of resistors R6 (1M) divided by R12 (220) if the circuit is driven from a very low impedance. However the driving source impedance is not low in this circuit and adds to the R12 resistance reducing the gain of the opamp. At maximum sensitivity setting, R5 (560) and R2 (470) are in series with R12 so the DC gain is 800.
3) C8 (10nF) across R6 (1M) cuts-off frequencies above 16Hz, so A1 will have a maximum gain of 800 at about 3.2Hz, 566 at 16Hz, 400 at 32 Hz and 200 at 64Hz etc.
4) The article should say, "The VCO operates through-out the audio-frequency range".
5) TR3 is used as a current amplifier and drives the speaker through R4, since the power output of A3 is not nearly enough to drive a speaker.
6) The 4.7K pot is the project's sensitivity control and is adjusted so that the circuit ignores external electromagnetic fields (from mains wiring and local AM, FM and TV stations).
7) The 8 ohm speaker produces the tone from the VCO. The higher the pitch, then the higher is the signal level that the project is picking-up. This project is not a radio and will not reproduce voices.
